U.S. patent application number 17/473087 was filed with the patent office on 2022-03-17 for salt bath systems for strengthening glass articles and methods for regenerating molten salt.
The applicant listed for this patent is CORNING INCORPORATED. Invention is credited to Sinue Gomez-Mower, Kenneth Edward Hrdina, Kai Tod Paul Jarosch, Yuhui Jin, Tyler John Lucci, Wei Sun, Madison Kathleen Tindle.
Application Number | 20220081357 17/473087 |
Document ID | / |
Family ID | |
Filed Date | 2022-03-17 |
United States Patent
Application |
20220081357 |
Kind Code |
A1 |
Gomez-Mower; Sinue ; et
al. |
March 17, 2022 |
SALT BATH SYSTEMS FOR STRENGTHENING GLASS ARTICLES AND METHODS FOR
REGENERATING MOLTEN SALT
Abstract
Embodiments of the present disclosure are directed to salt bath
systems for strengthening glass articles including a salt bath tank
defining a first interior volume enclosed by at least one sidewall;
a salt bath composition including an alkali metal salt positioned
within the first interior volume; a containment device defining a
second interior volume enclosed by at least one sidewall and
including a regeneration medium positioned within the second
interior volume; and a circulation device positioned proximate to
an inlet of the containment device, wherein the circulation device
is operable to circulate the salt bath composition through the
containment device. Methods for regenerating a molten salt are also
disclosed.
Inventors: |
Gomez-Mower; Sinue;
(Corning, NY) ; Hrdina; Kenneth Edward;
(Horseheads, NY) ; Jarosch; Kai Tod Paul;
(Corning, NY) ; Jin; Yuhui; (Painted Post, NY)
; Lucci; Tyler John; (Evanston, IL) ; Sun;
Wei; (Painted Post, NY) ; Tindle; Madison
Kathleen; (Painted Post, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CORNING INCORPORATED |
Corning |
NY |
US |
|
|
Appl. No.: |
17/473087 |
Filed: |
September 13, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
63078488 |
Sep 15, 2020 |
|
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International
Class: |
C03C 21/00 20060101
C03C021/00 |
Claims
1. A salt bath system for strengthening glass articles, the salt
bath system comprising: a salt bath tank defining a first interior
volume enclosed by at least one sidewall; a salt bath composition
comprising an alkali metal salt positioned within the first
interior volume; a containment device positioned within the first
interior volume, wherein the containment device defines a second
interior volume enclosed by at least one sidewall and comprises a
regeneration medium positioned within the second interior volume;
and a circulation device positioned proximate to an inlet of the
containment device, wherein the circulation device is operable to
circulate the salt bath composition through the containment
device.
2. The salt bath system of claim 1, wherein the regeneration medium
comprises silicic acid aggregates, an alkali metal phosphate salt,
a porous metal oxide, or combinations thereof.
3. The salt bath system of claim 1, wherein the average particle
size of the regeneration medium is from 5 .mu.m to 5,000 .mu.m.
4. The salt bath system of claim 1, wherein greater than or equal
to 90% of the regeneration medium have a particle size greater than
5 .mu.m.
5. The salt bath system of claim 1, wherein the regeneration medium
comprises grains, rings, saddles, spheres, engineered monoliths,
honeycombs, fibers, felts, active layers coated on or impregnated
in an inert carrier, or combinations of these.
6. The salt bath system of claim 1, wherein the salt bath
composition positioned within the first interior volume is
substantially free of the regeneration material.
7. The salt bath system of claim 1, wherein the circulation device
comprises an impeller, a pump, a gas injection system, or
combinations thereof.
8. The salt bath system of claim 1, wherein the circulation device
is operable to circulate the salt bath composition through the
containment device at a rate of from 0.001 vol/hr to 10 vol/hr.
9. The salt bath system of claim 1, wherein: the inlet of the
containment device is enclosed by a sieve comprising openings
having effective diameters less than or equal to 15% of an average
particle size of the regeneration media; an outlet of the
containment device is enclosed by a sieve comprising openings
having effective diameters less than or equal to 15% of the average
particle size of the regeneration media; or both inlet of the
containment device and the outlet of the containment device are
enclosed by sieves comprising openings having effective diameters
less than or equal to 15% of the average particle size of the
regeneration media.
10. The salt bath system of claim 1, wherein the second interior
volume comprises a first regeneration zone and a second
regeneration zone positioned downstream of the first regeneration
zone.
11. The salt bath system of claim 10, wherein: the first
regeneration zone comprises a first regeneration medium; and the
second regeneration zone comprises a second regeneration medium
different than the first regeneration medium.
12. The salt bath system of claim 11, wherein the containment
device comprises a sieve positioned between the first regeneration
zone and the second regeneration zone, wherein the sieve comprises
openings having diameters less than the average particle size of at
least one of the first regeneration medium and the second
regeneration medium.
13. A salt bath system for strengthening glass articles, the salt
bath system comprising: a salt bath tank defining a first interior
volume enclosed by at least one sidewall; a salt bath composition
comprising an alkali metal salt positioned within the first
interior volume; a containment device positioned outside of the
first interior volume and fluidly coupled to the first interior
volume, wherein the containment device defines a second interior
volume enclosed by at least one sidewall and comprises a
regeneration medium positioned within the second interior volume;
and a circulation device positioned within the first interior
volume and proximate to an inlet of the containment device, wherein
the circulation device is operable to circulate the molten salt
bath through the containment device.
14. The salt bath system of claim 13, wherein a temperature of the
second interior volume is greater than or equal to 3.degree. C.
less than a temperature of the first interior volume.
15. The salt bath system of claim 13, wherein the regeneration
medium comprises silicic acid, an alkali metal phosphate salt, an
alkali metal carbonate a porous metal oxide, or combinations
thereof.
16. The salt bath system of claim 13, wherein the average particle
size of the regeneration medium is be from 5 .mu.m to 5,000
.mu.m.
17. The salt bath system of claim 13, wherein greater than or equal
to 90% of the regeneration medium have a particle size greater than
5 .mu.m.
18. The salt bath system of claim 13, wherein the regeneration
medium comprises grains, rings, saddles, spheres, engineered
monoliths, honeycombs, fibers, felts, active layers coated on or
impregnated in an inert carrier, or combinations of these.
19. The salt bath system of claim 13, wherein the salt bath
composition positioned within the first interior volume is
substantially free of the regeneration material.
20. The salt bath system of claim 13, wherein the circulation
device comprises an impeller, a pump, a gas injection system, or
combinations thereof.
21. The salt bath system of claim 13, wherein the circulation
device is operable to circulate the salt bath composition through
the containment device at a rate of from 0.001 vol/hr to 10
vol/hr.
22. The salt bath system of claim 13, wherein: the inlet of the
containment device is enclosed by a sieve comprising openings
having effective diameters less than or equal to 15% of an average
particle size of the regeneration media; an outlet of the
containment device is enclosed by a sieve comprising openings
having effective diameters less than or equal to 15% of the average
particle size of the regeneration media; or both inlet of the
containment device and the outlet of the containment device are
enclosed by sieves comprising openings having effective diameters
less than or equal to 15% of the average particle size of the
regeneration media.
23. The salt bath system of claim 13, wherein the second interior
volume comprises a first regeneration zone and a second
regeneration zone positioned downstream of the first regeneration
zone.
24. The salt bath system of claim 23, wherein: the first
regeneration zone comprises a first regeneration medium; and the
second regeneration zone comprises a second regeneration medium
different than the first regeneration medium.
25. The salt bath system of claim 24, wherein the containment
device comprises a sieve positioned between the first regeneration
zone and the second regeneration zone, wherein the sieve comprises
openings having diameters less than the average particle size of at
least one of the first regeneration medium and the second
regeneration medium.
26. A method for regenerating a molten salt, the method comprising:
circulating the molten salt through a containment device positioned
within a first interior volume of a salt bath tank, the molten salt
comprising one or more impurities formed during an ion exchange
process, and the containment device comprising a regeneration
medium positioned within a second interior volume defined by the
containment device; and contacting the molten salt with the
regeneration medium within the containment device, wherein the
contact reduces a concentration of the one or more impurities in
the molten salt.
27. The method of claim 26, wherein the one or more impurities
comprises lithium nitrate, an alkali metal nitrite, an alkali metal
oxide, an alkaline earth metal nitrite, an alkaline earth metal
oxide, or combinations of these.
28. The method of claim 26, wherein the regeneration medium
comprises silicic acid, an alkali metal phosphate salt, an alkali
metal carbonate a porous metal oxide, or combinations of these.
29. The method of claim 26, wherein the average particle size of
the regeneration medium is be from 5 .mu.m to 5,000 .mu.m.
30. The method of claim 26, wherein greater than or equal to 90% of
the regeneration medium have a particle size greater than 5
.mu.m.
31. The method of claim 26, wherein the regeneration medium
comprises grains, rings, saddles, spheres, engineered monoliths,
honeycombs, fibers, felts, active layers coated on or impregnated
in an inert carrier, or combinations of these.
32. The method of claim 26, wherein the salt bath composition
positioned within the first interior volume is substantially free
of the regeneration material.
33. The method of claim 26, wherein the molten salt is circulated
through the containment device at a rate of from 0.001 vol/hr to 10
vol/hr.
34. The method of claim 26, further comprising: heating a salt bath
composition comprising an alkali metal salt to an ion exchange
temperature to form the molten salt; and submerging a glass article
into the molten salt such that an ion exchange between the molten
salt and the glass article occurs, wherein the ion exchange between
the molten salt and the glass article forms the one or more
impurities in the molten salt.
35. A method for regenerating a molten salt, the method comprising:
circulating the molten salt through a containment device positioned
outside of a first interior volume defined by a salt bath tank, the
molten salt comprising one or more impurities formed during an ion
exchange process, and the containment device comprising a
regeneration medium positioned within a second interior volume
defined by the containment device; and contacting the molten salt
with the regeneration medium within the containment device, wherein
the contact reduces a concentration of the one or more impurities
in the molten salt.
36. The method of claim 35, wherein a temperature of the second
interior volume is greater than or equal to 3.degree. C. less than
a temperature of the first interior volume.
37. The method of claim 35, wherein the one or more impurities
comprises lithium nitrate, an alkali metal nitrite, an alkali metal
oxide, an alkaline earth metal nitrite, an alkaline earth metal
oxide, or combinations of these.
38. The method of claim 35, wherein the regeneration medium
comprises silicic acid, an alkali metal phosphate salt, an alkali
metal carbonate a porous metal oxide, or combinations of these.
39. The method of claim 35, wherein the average particle size of
the regeneration medium is be from 5 .mu.m to 5,000 .mu.m.
40. The method of claim 35, wherein greater than or equal to 90% of
the regeneration medium have a particle size greater than 5
.mu.m.
41. The method of claim 35, wherein the regeneration medium
comprises grains, rings, saddles, spheres, engineered monoliths,
honeycombs, fibers, felts, active layers coated on or impregnated
in an inert carrier, or combinations of these.
42. The method of claim 35, wherein the salt bath composition
positioned within the first interior volume is substantially free
of the regeneration material.
43. The method of claim 35, wherein the molten salt is circulated
through the containment device at a rate of from 0.001 vol/hr to 10
vol/hr.
44. The method of claim 35, further comprising: heating a salt bath
composition comprising an alkali metal salt to an ion exchange
temperature to form the molten salt; and submerging a glass article
into the molten salt such that an ion exchange between the molten
salt and the glass article occurs, wherein the ion exchange between
the molten salt and the glass article forms the one or more
impurities in the molten salt.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of priority under 35
U.S.C. .sctn. 119 of U.S. Provisional Application Ser. No.
63/078,488 filed on Sep. 15, 2020, the content of which is relied
upon and incorporated herein by reference in its entirety.
BACKGROUND
Field
[0002] The present disclosure relates to systems and methods for
chemically strengthening glass articles and, in particular, salt
bath systems for strengthening glass articles and methods for
regenerating molten salt.
Technical Background
[0003] Tempered or strengthened glass may be used in a variety of
applications. For example, strengthened glass articles may be used
in consumer electronic devices, such as smart phones and tablets,
and pharmaceutical packaging because of its physical durability and
resistance to breakage. Conventional strengthening processes, such
as conventional ion exchange processes, often immerse multiple
glass articles in a single salt bath in batches to increase the
efficiency of the strengthening process. However, as the batchwise
production of strengthened glass articles continues in the same
salt bath, the ion exchange process will naturally result in a
decrease in the efficacy of the salt bath. While a number of
methods for reducing and/or preventing decreases in the efficacy of
the salt bath may be employed, these methods may also introduce
various complications to the ion exchange process.
[0004] Accordingly, a need exists for alternative salt bath systems
for strengthening glass articles as well as alternative methods for
regenerating molten salt.
SUMMARY
[0005] According to a first aspect of the present disclosure, a
salt bath system for strengthening glass articles may include a
salt bath tank defining a first interior volume enclosed by at
least one sidewall; a salt bath composition including an alkali
metal salt positioned within the first interior volume; a
containment device positioned within the first interior volume,
wherein the containment device defines a second interior volume
enclosed by at least one sidewall and includes a regeneration
medium positioned within the second interior volume; and a
circulation device positioned proximate to an inlet of the
containment device, wherein the circulation device is operable to
circulate the salt bath composition through the containment
device.
[0006] According to a second aspect of the present disclosure, a
salt bath system for strengthening glass articles may include a
salt bath tank defining a first interior volume enclosed by at
least one sidewall; a salt bath composition including an alkali
metal salt positioned within the first interior volume; a
containment device positioned outside of the first interior volume
and fluidly coupled to the first interior volume, wherein the
containment device defines a second interior volume enclosed by at
least one sidewall and includes a regeneration medium positioned
within the second interior volume; and a circulation device
positioned within the first interior volume and proximate to an
inlet of the containment device, wherein the circulation device is
operable to circulate the molten salt bath through the containment
device.
[0007] A third aspect of the present disclosure may include the
second aspect, wherein a temperature of the second interior volume
is greater than or equal to 3.degree. C. less than a temperature of
the first interior volume.
[0008] A fourth aspect of the present disclosure may include any of
the first through third aspects, wherein the regeneration medium
includes silicic acid aggregates, an alkali metal phosphate salt, a
porous metal oxide, or combinations thereof.
[0009] A fifth aspect of the present disclosure may include any of
the first through fourth aspects, wherein the average particle size
of the regeneration medium is from 5 .mu.m to 5,000 .mu.m.
[0010] A sixth aspect of the present disclosure may include any of
the first through fifth aspects, wherein greater than or equal to
90% of the regeneration medium have a particle size greater than 5
.mu.m.
[0011] A seventh aspect of the present disclosure may include any
of the first through sixth aspects, wherein the regeneration medium
includes grains, rings, saddles, spheres, engineered monoliths,
honeycombs, fibers, felts, active layers coated on or impregnated
in an inert carrier, or combinations of these.
[0012] An eighth aspect of the present disclosure may include any
of the first through seventh aspects, wherein the salt bath
composition positioned within the first interior volume is
substantially free of the regeneration material.
[0013] A ninth aspect of the present disclosure may include any of
the first through eighth aspects, wherein the circulation device
includes an impeller, a pump, a gas injection system, or
combinations thereof.
[0014] A tenth aspect of the present disclosure may include any of
the first through ninth aspects, wherein the circulation device is
operable to circulate the salt bath composition through the
containment device at a rate of from 0.001 vol/hr to 10 vol/hr.
[0015] An eleventh aspect of the present disclosure may include any
of the first through tenth aspects, wherein the inlet of the
containment device is enclosed by a sieve comprising openings
having effective diameters less than or equal to 15% of an average
particle size of the regeneration media; an outlet of the
containment device is enclosed by a sieve comprising openings
having effective diameters less than or equal to 15% of the average
particle size of the regeneration media; or both inlet of the
containment device and the outlet of the containment device are
enclosed by sieves comprising openings having effective diameters
less than or equal to 15% of the average particle size of the
regeneration media.
[0016] A twelfth aspect of the present disclosure may include any
of the first through eleventh aspects, wherein the second interior
volume comprises a first regeneration zone and a second
regeneration zone positioned downstream of the first regeneration
zone.
[0017] A thirteenth aspect of the present disclosure may include
the twelfth aspect, wherein the first regeneration zone comprises a
first regeneration medium; and the second regeneration zone
comprises a second regeneration medium different than the first
regeneration medium.
[0018] A fourteenth aspect of the present disclosure may include
the thirteenth aspect, wherein the containment device includes a
sieve positioned between the first regeneration zone and the second
regeneration zone, wherein the sieve includes openings having
diameters less than the average particle size of at least one of
the first regeneration medium and the second regeneration
medium.
[0019] According to a fifteenth aspect of the present disclosure,
method for regenerating a molten salt may include circulating the
molten salt through a containment device positioned within a first
interior volume of a salt bath tank, the molten salt including one
or more impurities formed during an ion exchange process, and the
containment device including a regeneration medium positioned
within a second interior volume defined by the containment device;
and contacting the molten salt with the regeneration medium within
the containment device, wherein the contact reduces a concentration
of the one or more impurities in the molten salt.
[0020] According to a sixteenth aspect of the present disclosure,
method for regenerating a molten salt may include circulating the
molten salt through a containment device positioned outside of a
first interior volume defined by a salt bath tank, the molten salt
including one or more impurities formed during an ion exchange
process, and the containment device including a regeneration medium
positioned within a second interior volume defined by the
containment device; and contacting the molten salt with the
regeneration medium within the containment device, wherein the
contact reduces a concentration of the one or more impurities in
the molten salt.
[0021] A seventeenth aspect of the present disclosure may include
the sixteenth aspect, wherein a temperature of the second interior
volume is greater than or equal to 3.degree. C. less than a
temperature of the first interior volume.
[0022] An eighteenth aspect of the present disclosure may include
any of the fifteenth through seventeenth aspects, wherein the one
or more impurities comprises lithium nitrate, an alkali metal
nitrite, an alkali metal oxide, an alkaline earth metal nitrite, an
alkaline earth metal oxide, or combinations of these.
[0023] A nineteenth aspect of the present disclosure may include
any of the fifteenth through eighteenth aspects, wherein the
regeneration medium comprises silicic acid, an alkali metal
phosphate salt, an alkali metal carbonate a porous metal oxide, or
combinations of these.
[0024] A twentieth aspect of the present disclosure may include any
of the fifteenth through nineteenth aspects, wherein the average
particle size of the regeneration medium is be from 5 .mu.m to
5,000 .mu.m.
[0025] A twenty-first aspect of the present disclosure may include
any of the fifteenth through twentieth aspects, wherein greater
than or equal to 90% of the regeneration medium have a particle
size greater than 5 .mu.m.
[0026] A twenty-second aspect of the present disclosure may include
any of the fifteenth through twenty-first aspects, wherein the
regeneration medium comprises grains, rings, saddles, spheres,
engineered monoliths, honeycombs, fibers, felts, active layers
coated on or impregnated in an inert carrier, or combinations of
these.
[0027] A twenty-third aspect of the present disclosure may include
any of the fifteenth through twenty-second aspects, wherein the
salt bath composition positioned within the first interior volume
is substantially free of the regeneration material.
[0028] A twenty-fourth aspect of the present disclosure may include
any of the fifteenth through twenty-third aspects, wherein the
molten salt is circulated through the containment device at a rate
of from 0.001 vol/hr to 10 vol/hr.
[0029] A twenty-fifth aspect of the present disclosure may include
any of the fifteenth through twenty-fourth aspects, further
including heating a salt bath composition comprising an alkali
metal salt to an ion exchange temperature to form the molten salt;
and submerging a glass article into the molten salt such that an
ion exchange between the molten salt and the glass article occurs,
wherein the ion exchange between the molten salt and the glass
article forms the one or more impurities in the molten salt.
[0030] It is to be understood that both the foregoing general
description and the following detailed description describe various
embodiments and are intended to provide an overview or framework
for understanding the nature and character of the claimed subject
matter. The accompanying drawings are included to provide a further
understanding of the various embodiments, and are incorporated into
and constitute a part of this specification. The drawings
illustrate the various embodiments described herein, and together
with the description serve to explain the principles and operations
of the claimed subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] The following detailed description of the present disclosure
may be better understood when read in conjunction with the
following drawings in which:
[0032] FIG. 1A schematically depicts a portion of an ion exchange
process, according to one or more embodiments shown and described
herein;
[0033] FIG. 1B schematically depicts a portion of an ion exchange
process, according to one or more embodiments shown and described
herein;
[0034] FIG. 2A schematically depicts a portion of an ion exchange
process, according to one or more embodiments shown and described
herein;
[0035] FIG. 2B schematically depicts a portion of an ion exchange
process, according to one or more embodiments shown and described
herein;
[0036] FIG. 3A schematically depicts a portion of an ion exchange
process, according to one or more embodiments shown and described
herein;
[0037] FIG. 3B schematically depicts a portion of an ion exchange
process, according to one or more embodiments shown and described
herein;
[0038] FIG. 4A schematically depicts a generalized flow diagram of
a salt bath system for strengthening glass articles, according to
one or more embodiments shown and described herein;
[0039] FIG. 4B schematically depicts a generalized flow diagram of
a salt bath system for strengthening glass articles, according to
one or more embodiments shown and described herein;
[0040] FIG. 4C schematically depicts a containment device of the
salt bath systems for strengthening glass articles depicted in
FIGS. 4B and 4C, according to one or more embodiments shown and
described herein;
[0041] FIG. 5A graphically plots Surface Hydrolytic Resistance
titrant volume (mL; y-axis) as a function of time (days; x-axis)
for salt bath systems for strengthening glass articles using
various amounts of a regeneration medium, according to one or more
embodiments shown and described herein;
[0042] FIG. 5B graphically plots Surface Hydrolytic Resistance
titrant volume (mL; y-axis) as a function of the number of glass
articles strengthened (vials per kilogram of alkali metal salt;
x-axis) for salt bath systems for strengthening glass articles
using various amounts of a regeneration medium, according to one or
more embodiments shown and described herein;
[0043] FIG. 6A graphically plots surface compressive stress (MPa;
left y-axis) and depth of compression (.mu.m; right y-axis) as a
function of time (days; x-axis) for a salt bath system for
strengthening glass articles, according to one or more embodiments
shown and described herein; and
[0044] FIG. 6B graphically plots surface compressive stress (MPa;
left y-axis) and depth of compression (.mu.m; right y-axis) as a
function of the number of glass articles strengthened (vials per
kilogram of alkali metal salt; x-axis) for a salt bath system for
strengthening glass articles, according to one or more embodiments
shown and described herein.
[0045] When describing the simplified schematic illustration of
FIGS. 4A-4C, the numerous valves, temperature sensors, electronic
controllers, and the like, which may be used and are well known to
a person of ordinary skill in the art, are not included. However, a
person of ordinary skill in the art understands that these
components are within the scope of the present disclosure.
[0046] Additionally, the arrows in the simplified schematic
illustration of FIGS. 4A-4C refer to the transfer or flow of
materials. However, the arrows may equivalently refer to transfer
lines, such as conduits or the like, which may transfer such
materials between two or more system components. Arrows that
connect to one or more system components signify inlets or outlets
in the given system components and arrows that connect to only one
system component signify a system outlet that exits the depicted
system or a system inlet that enters the depicted system. The arrow
direction generally corresponds with the major direction of
movement of the materials or the materials contained within the
physical transfer line signified by the arrow.
[0047] The arrows in the simplified schematic illustration of FIGS.
4A-4C may also refer to process steps of transporting materials
from one system component to another system component. For example,
an arrow from a first system component pointing to a second system
component may signify "passing" materials from the first system
component to the second system component, which may comprise the
materials "exiting" or being "removed" from the first system
component and "introducing" the materials to the second system
component.
[0048] Reference will now be made in greater detail to various
embodiments of the present disclosure, some of which are
illustrated in the accompanying drawings.
DETAILED DESCRIPTION
[0049] Embodiments described herein are directed to salt bath
systems for strengthening glass articles and methods for
regenerating molten salt. Salt bath systems for strengthening glass
articles according to the present disclosure may generally comprise
a salt bath tank defining a first interior volume enclosed by at
least one sidewall, a salt bath composition positioned within the
first interior volume, a containment device positioned within the
first interior volume, and a circulation device positioned
proximate to an inlet of the containment device. The salt bath
composition may comprise an alkali metal salt. The containment
device may define a second interior volume enclosed by at least one
sidewall and may comprise a regeneration medium positioned within
the second interior volume. The circulation device may be operable
to circulate the salt bath composition through the containment
device. Methods for regenerating molten salt according to the
present disclosure may generally comprise circulating the molten
salt through a containment device positioned within a first
interior volume of a salt bath tank, and contacting the molten salt
with the regeneration medium within the containment device. The
molten salt may comprise one or more impurities formed during an
ion exchange process. The containment device may comprise a
regeneration medium positioned within a second interior volume
defined by the containment device. The contact may reduce a
concentration of the one or more impurities in the molten salt.
Various embodiments of the systems and methods of the present
disclosure will be described herein with specific reference to the
appended drawings.
[0050] Directional terms as used herein--for example up, down,
right, left, front, back, top, bottom--are made only with reference
to the figures as drawn and are not intended to imply ab solute
orientation.
[0051] As used herein, the indefinite articles "a" and "an," when
referring to elements of the present disclosure, mean that least
one of these elements are present. Although these indefinite
articles are conventionally employed to signify that the modified
noun is a singular noun, the indefinite articles "a" and "an" also
include the plural in the present disclosure, unless stated
otherwise. Similarly, the definite article "the" also signifies
that the modified noun may be singular or plural in the present
disclosure, unless stated otherwise.
[0052] As used herein, the term "or" is inclusive and, in
particular, the term "A or B" refers to "A, B, or both A and B."
Alternatively, the term "or" may be used in the exclusive sense
only when explicitly designated in the present disclosure, such as
by the terms "either A or B" or "one of A or B."
[0053] As used herein, the terms "salt bath composition," "salt
bath," "molten salt," etc., are, unless otherwise specified,
equivalent terms, and refer to the solution or medium used to
effect the ion exchange process with a glass (or glass-ceramic)
article, in which cations within the surface of a glass article are
replaced or exchanged with cations that are present in the salt
bath. It is understood that a salt bath may include at least one
alkali metal salt, such as potassium nitrate (KNO.sub.3) and/or
sodium nitrate (NaNO.sub.3), which may be liquefied by heat or
otherwise heated to a substantially liquid phase.
[0054] As used herein, the term "chemical durability" refers to the
ability of the glass composition to resist degradation upon
exposure to specified chemical conditions. Specifically, the
chemical durability of the glass articles described herein was
assessed in water according to the "Surface Glass Test" of USP
<660>"Containers--Glass" (2017).
[0055] It should be understood that a flow of materials may be
named for the components within the flow of materials, and the
component for which the flow of materials is named may be the major
component of the flow of materials (such as comprising from 50 wt.
%, from 70 wt. %, from 90 wt. %, from 95 wt. %, from 99 wt. %, from
99.5 wt. %, or from 99.9 wt. % of the flow of materials to 100 wt.
% of the flow of materials). For example, a flow of a salt bath
composition, which may be from a salt bath tank to a containment
device, may comprise from 50 wt. % to 100 wt. % of the salt bath
composition and, as a result, the flow of materials may also be
named the "salt bath composition." It should also be understood
that components are disclosed as passing from one system component
to another when a flow of materials comprising that component is
disclosed as passing from that system component to another. For
example, a disclosed flow of a salt bath composition from a first
system component to a second system component should be understood
to equivalently disclose the salt bath composition passing from the
first system component to the second system component.
[0056] Unless otherwise expressly stated, it is in no way intended
that any method set forth herein be construed as requiring that its
steps be performed in a specific order, nor that with any apparatus
specific orientations be required. Accordingly, where a method
claim does not actually recite an order to be followed by its
steps, or that any apparatus claim does not actually recite an
order or orientation to individual components, or it is not
otherwise specifically stated in the claims or description that the
steps are to be limited to a specific order, or that a specific
order or orientation to components of an apparatus is not recited,
it is in no way intended that an order or orientation be inferred,
in any respect. This holds for any possible non-express basis for
interpretation, including: matters of logic with respect to
arrangement of steps, operational flow, order of components, or
orientation of components; plain meaning derived from grammatical
organization or punctuation, and; the number or type of embodiments
described in the specification.
[0057] Referring initially to FIGS. 1A and 1B, a conventional ion
exchange process is schematically depicted. The ion exchange
process includes immersing a glass article 105 in a salt bath 100.
The glass article 105 may contain relatively smaller cations 130,
for example, alkali metal cations such as Li.sup.+ and/or Na.sup.+
cations. The salt bath 100 may include a molten salt 101 containing
relatively larger cations 120 (i.e., relative to the cations 130 of
the glass article). That is, the cations 120 may have an atomic
radius larger than an atomic radius of the cations 130. The cations
120 may include, for example, alkali metal cations, such as
potassium (K.sup.+) cations. The larger cations 120 may have
disassociated from a salt, such as an alkali metal nitrate, present
in the salt bath 100 when heated to an elevated temperature to
produce the molten salt 101. When the glass article 105 is immersed
in the salt bath 100, the cations 130 within the glass article 105
may diffuse from the glass article 105 and into the molten salt
101. Referring now to FIG. 1B, the cations 120 from the molten salt
101 may replace the cations 130 in the glass article 105 after such
diffusion. This substitution of larger cations from the molten salt
101 for smaller cations in the glass article 105 creates a surface
compressive stress (CS) at the surface of the glass article 105
that extends to a depth of compression (DOC), which may increase
the mechanical strength of the glass article 105 and improve the
resistance of the glass article 105 to breakage.
[0058] Generally, multiple glass articles may be immersed in a
single salt bath in batches in order to increase the efficiency of
the ion exchange process. However, as the batchwise production of
strengthened glass articles continues in the same salt bath, the
ion exchange process will naturally result in a decrease in the
efficacy of the salt bath. One reason for this decrease in the
efficacy of the salt bath may be due to the formation of
undesirable species within the molten salt. In particular, during
an ion exchange process, alkali metal nitrates present in the salt
bath may decompose into alkali metal nitrites and/or alkali metal
oxides in the molten salt. For example, the decomposition of an
alkali metal nitrate into an alkali metal nitrite is indicated in
the following equation:
MNO.sub.3.rarw..fwdarw.MNO.sub.2+1/2O.sub.2 [M: IUPAC Group 1
Metal]
[0059] Both alkali metal nitrates and alkali metal nitrites may
further decompose into alkali metal oxides, as indicated in the
following equation:
MNO.sub.2.rarw..fwdarw.M.sub.2O+NO.sub.x [M: IUPAC Group 1
Metal]
For example, in instances where potassium nitrate (KNO.sub.3) is
present in the salt bath, the KNO.sub.3 decomposes into two primary
decomposition products at temperatures greater than about
400.degree. C.: potassium nitrite (KNO.sub.2) and potassium oxide
(K.sub.2O). Other alkali metal nitrates, such as sodium nitrate and
lithium nitrate, may decompose into the corresponding alkali metal
nitrites and alkali metal oxides at temperatures even lower than
KNO.sub.3 (i.e., temperatures less than or equal to 400.degree.
C.
[0060] The presence of alkali metal oxides, such as K.sub.2O, in
the molten salt may degrade the properties of the glass articles
treated therein. In particular, alkali metal oxides in the molten
salt may incongruently etch the surface of glass articles during
ion exchange. This etching may degrade the surface of the glass
article, which may, in turn, adversely impact a number of
properties of the glass article. For example, glass articles that
undergo ion exchange in molten salt that includes concentrations of
K.sub.2O greater than or equal to 0.5 wt. % may form visible
etching and surface damage on the glass articles. Even when glass
articles undergo ion exchange in molten salt that includes
concentrations of K.sub.2O significantly less than 0.5 wt. % (i.e.,
0.05 wt. % or even 0.005 wt. %), the presence of K.sub.2O may
result in a substantial decrease in the mechanical strength of the
glass articles.
[0061] The degradation of the surface of glass articles during ion
exchange may be reduced or prevented by the neutralization of the
salt bath. That is, the degradation of the surface of glass
articles during ion exchange may be reduced or prevented by a
reduction or elimination of the alkali metal oxides present within
the salt bath. This may be achieved, at least in part, by the
inclusion of a regeneration medium, such as silicic acid, within
the salt bath. As used herein, the term "silicic acid" may refer to
silicic acids, such as orthosilicic acid (Si(OH).sub.4), as well as
the corresponding silicates, which are the conjugate bases of
silicic acids. Silicic acids generally react with alkali metal
oxides to form an unreactive product, as indicated in the following
equation:
M.sub.2O+SiO.sub.2.fwdarw.M.sub.2SiO.sub.3 [M: IUPAC Group 1
Metal]
Silicic acid may also react with common contaminants in the molten
salt, such as calcium cations (Ca.sup.2+) and magnesium cations
(Mg.sup.2+), which can attach to the surfaces of glass articles and
retard ion exchange processes.
[0062] Another reason for this decrease in efficacy of the salt
bath may be due to the "poisoning" of the molten salt with
undesirable cations initially present in the glass articles. For
example, while lithium-containing glass articles may provide a
number of benefits, such as a quicker and more efficient ion
exchange process, as few as 1 wt. % of lithium cations in the
molten salt bath (i.e., lithium cations exchanged out of the glass
article and into the slat bath during ion exchange) may reduce the
surface compressive stress and depth of compression achievable in
the glass articles. Even when the concentration of lithium cations
in the molten salt is less than 1 wt. %, lithium cations may retard
the ion exchange process and, as the concentration of lithium
cations in the molten salt naturally increases during the ion
exchange process, results in strengthened glass articles with
drastically different compressive stresses and depths of
compression from batch to batch.
[0063] Salt baths that have been poisoned with undesirable cations,
such as lithium cations, may be regenerated by the addition of a
regeneration medium, such as a phosphate salt. For example,
referring now to FIGS. 2A and 2B, a salt bath 200 containing a
poisoned molten salt 202 is depicted. The poisoned molten salt 202
contains lithium cations 230 and relatively larger cations 220
(i.e., relative to the lithium cations 230 of the glass article),
such as, for example, sodium and/or potassium cations. The poisoned
molten salt 202 may be regenerated by adding a phosphate salt 240.
When introduced to the poisoned molten salt 202, the phosphate salt
240 may disassociate to form cations and phosphate
(PO.sub.4.sup.-3) anions. The phosphate anions present in the
poisoned molten bath 202 may react with and selectively precipitate
the lithium cations 230. The selective precipitation reaction
produces insoluble lithium phosphates 250, such as, for example,
trilithium phosphate (Li.sub.3PO.sub.4), dilithium sodium phosphate
(Li.sub.2NaPO.sub.4), and/or lithium disodium phosphate
(LiNa.sub.2PO.sub.4), and a regenerated molten salt 211 that is
suitable for use in further ion exchange processes. In other words,
the presence of the phosphate salt creates favorable conditions for
the removal of lithium cations from the salt bath via
precipitation.
[0064] In particular, a poisoned molten salt may be regenerated by
"spiking" the salt bath with a phosphate salt (i.e., introducing a
phosphate salt between batches), as depicted in FIGS. 2A and 2B, or
a phosphate salt may be present during the ion exchange process, as
depicted in FIGS. 3A and 3B. For example, a glass article 305
containing lithium cations 330 may be immersed in a salt bath 300
containing relatively larger cations 320 (i.e., relative to the
lithium cations 330 of the glass article), such as, for example,
sodium and/or potassium cations, and a phosphate salt 340. As the
lithium cations 330 diffuse from the glass article 305, the
phosphate anions that have disassociated from the phosphate salt
340 may react with and selectively precipitate the dissolved
lithium cations 230 to produce insoluble lithium phosphates 350 and
a regenerated molten salt 311.
[0065] As indicated hereinabove, a number of methods for reducing
and/or preventing decreases in the efficacy of the salt bath may be
employed. However, while the introduction of regeneration media,
such as silicic acid and/or phosphate salts, may reduce and/or
prevent decreases in the efficacy of the salt bath resulting from
the ion exchange process, these regeneration media may introduce
new complications to the ion exchange process.
[0066] For example, when silicic acid particles that are too large
are added to a salt bath, the silicic acid may fail to effectively
neutralize the molten salt. In particular, when the silicic acid
particles have an average size that is too large the silicic acid
particles may sink more quickly to the bottom of the molten salt
and, as a result, the probability of interactions and reactions
between the silicic acid and the alkali metal oxides may be
reduced. The large silicic acid particles may also accumulate as a
sludge at the bottom of the salt bath over time until the system
must be shut down and the salt bath must be replaced. Conversely,
when the average particle size of the silicic acid particles is too
small, the silicic acid particles may adhere to the surfaces of
glass articles that are ion exchanged in the molten salt. This
adhesion of silicic acid particles to the surfaces of the glass
articles may result in defects that render the glass articles
unsuitable for commercial use or, at least, require additional
processing that increases production costs and reduces
efficiency.
[0067] Similarly, the addition of phosphate salts to a salt bath
may result in the formation of an insoluble sludge that must be
removed from the salt bath and/or phosphate crystals that may
adhere to the glass articles. For example, while lithium cations
preferably bond with the phosphate salt over other alkali metal
cations present in the salt bath, such as sodium and potassium
cations, the phosphate salt may begin to react with the other
alkali metal cations to form alkali metal phosphate salts, which
may associate to form phosphate crystals, as the lithium cation
concentration decreases. The phosphate crystals may adhere to the
surfaces of glass articles that are ion exchanged in the molten
salt. The presence of the phosphate crystals on the surfaces of the
glass articles may retard the ion exchange process, reducing the
compressive stress and depth of compression achieved, and may
result in the formation of depressions and/or protrusions on the
surfaces of the glass articles upon removal. Even when the
formation of the phosphate crystals is minimized, the insoluble
lithium phosphates will build in the salt bath over time, which
requires the periodic stoppage of the process in order to remove
the sludge and restore the salt bath to the original
composition.
[0068] The present disclosure is directed to salt bath systems for
strengthening glass articles and methods for regenerating molten
salts that utilize regeneration media, such as silicic acid and/or
phosphate salts, to effectively regenerate molten salts while also
reducing or preventing the undesirable effects associated with the
presence of these regeneration media in the molten salt.
[0069] Referring now to FIGS. 4A and 4B, a salt bath system 400 is
schematically depicted. The salt bath system 400 may include a salt
bath tank 402. The salt bath tank 402 may define a first interior
volume 404 enclosed by at least one sidewall 406 and a salt bath
composition 408 may be positioned within the first interior volume
404. The salt bath system 400 may further include a containment
device 410 positioned within the first interior volume 404. The
containment device 410 may define a second interior volume 412
enclosed by at least one sidewall 414. One or more regeneration
media may be positioned within the second interior volume 412. The
salt bath system may further include a circulation device 416
positioned proximate to an inlet 418 of the containment device
410.
[0070] In embodiments, the salt bath composition 408 may comprise
an alkali metal salt. For example, the salt bath composition 408
may comprise an alkali metal nitrate, such as potassium nitrate
(KNO.sub.3), sodium nitrate (NaNO.sub.3), lithium nitrate
(LiNO.sub.3), or combinations thereof. In embodiments, the salt
bath composition 408 may comprise greater than or equal to 90 wt. %
of the one or more alkali metal salts based on the total weight of
the salt bath composition 408. For example, the salt bath
composition 408 may comprise from 90 wt. % to 99.9 wt. %, from 90
wt. % to 99.5 wt. %, from 90 wt. % to 99 wt. %, from 90 wt. % to 97
wt. %, from 90 wt. % to 95 wt. %, from 90 wt. % to 93 wt. %, from
93 wt. % to 99.9 wt. %, from 93 wt. % to 99.5 wt. %, from 93 wt. %
to 99 wt. %, from 93 wt. % to 97 wt. %, from 93 wt. % to 95 wt. %,
from 95 wt. % to 99.9 wt. %, from 95 wt. % to 99.5 wt. %, from 95
wt. % to 99 wt. %, from 95 wt. % to 97 wt. %, from 97 wt. % to 99.9
wt. %, from 97 wt. % to 99.5 wt. %, from 97 wt. % to 99 wt. %, from
99 wt. % to 99.9 wt. %, from 99 wt. % to 99.5 wt. %, or from 99.5
wt. % to 99.9 wt. % of the one or more alkali metal salts based on
the total weight of the salt bath composition 408.
[0071] In embodiments, the concentrations of the alkali metal salts
in the salt bath composition 408 may be balanced based on the
composition of the glass article to provide an ion exchange process
that increases both the surface compressive stress at the surface
of the glass article as well as the depth of compression after the
ion exchange process. For example, the salt bath composition 408
may comprise a greater concentration of potassium nitrate than
sodium nitrate based on the total concentration of the salt bath
composition 408, or the salt bath composition 408 may comprise a
greater concentration of sodium nitrate than potassium nitrate
based on the total concentration of the salt bath composition 408.
A greater concentration of sodium nitrate than potassium nitrate in
the salt bath composition, in conjunction with a longer residence
time in the molten salt bath, may result in a deeper depth of
compression in the glass article.
[0072] In embodiments, the salt bath composition 408 may optionally
comprise lithium nitrate in an amount less than or equal to 1 wt. %
based on the total weight of the salt bath composition 408. For
example, the salt bath composition 408 may comprise lithium nitrate
in an amount of from 0.01 wt. % to 1 wt. %, from 0.01 wt. % to 0.8
wt. %, from 0.01 wt. % to 0.6 wt. %, from 0.01 wt. % to 0.3 wt. %,
from 0.01 wt. % to 0.2 wt. %, from 0.01 wt. % to 0.1 wt. %, from
0.1 wt. % to 1 wt. %, from 0.1 wt. % to 0.8 wt. %, from 0.1 wt. %
to 0.6 wt. %, from 0.1 wt. % to 0.3 wt. %, from 0.1 wt. % to 0.2
wt. %, from 0.2 wt. % to 1 wt. %, from 0.2 wt. % to 0.8 wt. %, from
0.2 wt. % to 0.6 wt. %, from 0.2 wt. % to 0.3 wt. %, from 0.3 wt. %
to 1 wt. %, from 0.3 wt. % to 0.8 wt. %, from 0.3 wt. % to 0.6 wt.
%, from 0.6 wt. % to 1 wt. %, from 0.6 wt. % to 0.8 wt. %, or from
0.8 wt. % to 1 wt. %, based on the total weight of the salt bath
100. When the concentration of lithium nitrate is too great (i.e.,
greater than 1 wt. %), either through the inclusion of lithium
nitrate in the salt bath composition and/or through the diffusion
of lithium cations from glass articles, the molten salt may be
considered poisoned, which adversely affects the ion exchange
process. Poisoned molten salt may lower the compressive stress and
depth of compression of glass articles when compared to glass
articles subjected to an ion exchange process in a molten salt that
is not poisoned. In contrast, when the concentration of lithium
nitrate is too low (i.e., less than 0.01 wt. %), the molten salt
bath may be unsuitable for the strengthening of some articles, such
as glass ceramic articles. In particular, excess lithium cations,
which may act as nucleating agents that facilitate the formation of
one or more crystalline phases, may diffuse from glass ceramic
articles during ion exchange processes, which may result in the
reduction of crystallization achieved and an increase in
sodium-rich regions in the glass ceramic articles. Sodium-rich
regions in the glass ceramic articles may lead to corrosion and/or
cracking of the glass ceramic articles.
[0073] The salt bath composition 408 may be used to effectuate an
ion exchange process, which exchanges metal cations of a glass
article with alkali metal cations of the alkali metal salts of the
salt bath composition 408. Once the salt bath composition 408 has
been positioned within the first interior volume 404, the salt bath
composition 408 may be heated to an elevated temperature (also
referred to as an ion exchange temperature) sufficient to create a
molten salt and thereby promote an ion exchange process. In
embodiments, the salt bath composition 408 may be heated to a
temperature of from 350.degree. C. to 500.degree. C. For example,
the salt bath composition may be heated to a temperature of from
350.degree. C. to 475.degree. C., from 350.degree. C. to
450.degree. C., from 350.degree. C. to 425.degree. C., from
350.degree. C. to 400.degree. C., from 350.degree. C. to
375.degree. C., from 375.degree. C. to 500.degree. C., from
375.degree. C. to 475.degree. C., from 375.degree. C. to
450.degree. C., from 375.degree. C. to 425.degree. C., from
375.degree. C. to 400.degree. C., from 400.degree. C. to
500.degree. C., from 400.degree. C. to 475.degree. C., from
400.degree. C. to 450.degree. C., from 400.degree. C. to
425.degree. C., from 425.degree. C. to 500.degree. C., from
425.degree. C. to 475.degree. C., from 425.degree. C. to
450.degree. C., from 450.degree. C. to 500.degree. C., from
450.degree. C. to 475.degree. C., or from 475.degree. C. to
500.degree. C. However, if the ion exchange temperature is too
high, it may be difficult to adequately control the ion exchange
process and, for example, the rate of degradation of the alkali
metal salts in the salt bath composition 408 may increase.
[0074] Referring still to FIG. 4A, the salt bath system 400 may
include a containment device 410 positioned in the first interior
volume 404. The containment device 410 may define a second interior
volume 412 enclosed by at least one sidewall 414. One or more
regeneration media may be positioned within the second interior
volume 412. The containment device 410 may allow for contact
between the salt bath composition 408 and the regeneration media
and, as a result, reduce and/or prevent any decreases in the
efficacy of the salt bath composition 408. Moreover, since all
and/or a substantial portion of the regeneration media used in the
salt bath system 400 is positioned within the containment device
410, any undesirable by-products of the one or more regeneration
media remains in the containment device 410.
[0075] As a result, the complications associated with the use of
regeneration media, such as silicic acid adhering to surfaces of
glass articles and/or insoluble lithium phosphate sludge building
up in the salt bath tank 402, may be reduced and/or prevented
entirely. In turn, the containment device 410 may significantly
increase the life of the salt bath composition 408 and the overall
throughput of the strengthening process, which may significantly
reduce operation costs. Moreover, since the regeneration media
remain separate from the salt bath composition 408, the
regeneration media may be removed, refreshed, and/or replaced as
they become depleted without replacing the salt bath composition
408. This may further increase the efficiency of the salt bath
system 400 compared to conventional salt bath systems that
introduce regeneration media directly into the salt bath
composition.
[0076] In embodiments, the containment device 410 may include any
vessel suitable for contact with molten salt (i.e., the salt bath
composition 408 heated to a temperature of from 350.degree. C. to
500.degree. C.) on both interior and exterior surfaces. For
example, in some embodiments, the containment device 410 may
include one or more sections of a size 8, schedule 10, Society of
Automotive Engineers (SAE) 304 stainless steel pipe. In other
embodiments (not depicted), the containment device 410 may include
one or more vessels, such as baskets and/or pouches, composed of
stainless steel mesh that allows for the flow of the salt bath
composition 408 through the containment device 410, but prevents
the displacement of the regeneration media.
[0077] As mentioned hereinabove, one or more regeneration media may
be positioned within the second interior volume 412 of the
containment device 410. As used herein, the term "regeneration
medium" refers to any material that is effective to precipitate,
filter, bind, reduce the concentration of, or remove from a molten
salt bath one or more materials formed during an ion exchange
process and/or considered to negatively affect the ion exchange of
a glass article or otherwise be undesirable in a salt bath
composition (also referred to as impurities and/or contaminants).
For example, the regeneration media may include silicic acid,
which, as noted hereinabove, react with and remove the
decomposition products of alkali metal salts from the salt bath
composition 408. Similarly, the regeneration media may include a
phosphate salt, which, as noted hereinabove, may precipitate excess
lithium cations from the salt bath composition 408. The
regeneration media may also include alkali metal carbonates, such
as potassium carbonate (K.sub.2CO.sub.3), which may be suitable for
sodium scrubbing (i.e., reducing sodium nitrate to an appropriate
concentration), and filtration media that may be suitable to remove
debris and contaminants from the salt bath composition 408.
[0078] The regeneration media may be in any form suitable for
packing in the containment device 410 while also allowing for the
adequate flow of the salt bath composition 408 through the
containment device 410. For example, the regeneration media include
grains, rings, saddles, spheres, engineered monoliths, honeycombs,
fibers, felts, active layers coated on or impregnated in an inert
carrier, or combinations of these. As described in detail herein,
the one or more regeneration media may be contained within the
containment device 410 via the side wall 414 as well as one or more
barriers disposed at both the inlet and outlet of the containment
device 410. The barriers, which may be one or more mesh layers, may
allow the flow of the salt bath composition 408 through the
containment device 410 such that the salt bath composition 408
contacts the regeneration media, but may prevent the displacement
of the regeneration media from the containment device 410 and into
the first interior volume 404 of the salt bath tank 402.
[0079] In embodiments wherein the regeneration media are granular,
the average particle size of the granular regeneration media may be
from 5 .mu.m to 5,000 .mu.m. For example, in embodiments wherein
the regeneration media are granular, the average particle size of
the granular regeneration media may be from 5 .mu.m to 2,000 .mu.m,
from 5 .mu.m to 1,000 .mu.m, from 5 .mu.m to 500 .mu.m, from 5
.mu.m to 100 .mu.m, from 5 .mu.m to 50 .mu.m, from 50 .mu.m to
5,000 .mu.m, from 50 .mu.m to 2,000 .mu.m, from 50 .mu.m to 1,000
.mu.m, from 50 .mu.m to 500 .mu.m, from 50 .mu.m to 100 .mu.m, from
100 .mu.m to 5,000 .mu.m, from 100 .mu.m to 2,000 .mu.m, from 100
.mu.m to 1,000 .mu.m, from 100 .mu.m to 500 .mu.m, from 500 .mu.m
to 5,000 .mu.m, from 500 .mu.m to 2,000 .mu.m, from 500 .mu.m to
1,000 .mu.m, from 1,000 .mu.m to 5,000 .mu.m, from 1,000 .mu.m to
2,000 .mu.m, or from 2,000 .mu.m to 5,000 .mu.m. In embodiments,
greater than or equal to 90% of the regeneration medium may have a
particle size greater than 5 .mu.m. For example, greater than or
equal to 92%, 94%, 96%, 98%, 99% or 99.5% of the regeneration
medium may have a particle size greater than 5 .mu.m When the
average particle size of the granular regeneration media is smaller
(i.e., less than 5 .mu.m), the regeneration may pack too tightly
and the pressure drop across the containment device 410 may be too
significant for the efficient operation of the salt bath system
400. Conversely, when the average particle size of the granular
regeneration media is larger (i.e., greater than 5 .mu.m), some
species, such as insoluble lithium phosphates, may favourably
precipitate onto the surface of the larger particles. This
decreases the amount of relatively smaller species that may be
capable of exiting the containment device 410 and contaminating the
salt bath composition 408.
[0080] In embodiments, the regeneration medium may include silicic
acid aggregates. As used herein, the term "silicic acid aggregate"
may refer to a cluster or unit formed by the collection of silicic
acid nanoparticles into a single mass. As described hereinabove,
the silicic acid aggregates may react with the decomposition
products of the one or more alkali metal salts in the salt bath
composition 408 to form an unreactive (e.g., does not etch or
corrode the surface of glass articles) silicate and water.
Accordingly, the silicic acid aggregates may reduce the
concentration of the decomposition products of the alkali metal
salts within the salt bath composition 408 and neutralize the salt
bath composition 408.
[0081] In embodiments, the silicic acid aggregates may have an
average particle size of from 5 .mu.m to 400 .mu.m, as measured by
laser diffraction particle size analysis. For example, the silicic
acid aggregates may have an average particle size of from 5 .mu.m
to 350 .mu.m, from 5 .mu.m to 300 .mu.m, from 5 .mu.m to 250 .mu.m,
from 5 .mu.m to 200 .mu.m, from 5 .mu.m to 50 .mu.m, from 50 .mu.m
to 400 .mu.m, from 50 .mu.m to 350 from 50 .mu.m to 300 from 50
.mu.m to 250 from 50 .mu.m to 200 from 200 .mu.m to 400 from 200
.mu.m to 350 from 200 .mu.m to 300 from 200 .mu.m to 250 from 250
.mu.m to 400 from 250 .mu.m to 350 from 250 .mu.m to 300 from 300
.mu.m to 400 from 300 .mu.m to 350 or from 350 .mu.m to 400 as
measured by laser diffraction particle size analysis. When the
silicic acid aggregates have a smaller average particle size (e.g.,
less than 5 .mu.m), any silicic acid aggregates that are displaced
from the containment device 410, due to any circumstance, may
readily adhere to the surface of glass articles and cause defects
that render the glass article unsuitable for commercial use.
[0082] In embodiments, the specific surface area of the silicic
acid aggregates may be greater than or equal to 200 m.sup.2/g, as
measured by the Brunauer-Emmett-Teller (BET) method. For example,
the specific surface area of the silicic acid aggregates may be
from 200 m.sup.2/g to 600 m.sup.2/g, from 200 m.sup.2/g to 550
m.sup.2/g, from 200 m.sup.2/g to 500 m.sup.2/g, from 200 m.sup.2/g
to 450 m.sup.2/g, from 200 m.sup.2/g to 400 m.sup.2/g, from 200
m.sup.2/g to 350 m.sup.2/g, from 200 m.sup.2/g to 300 m.sup.2/g,
from 200 m.sup.2/g to 250 m.sup.2/g, from 250 m.sup.2/g to 600
m.sup.2/g, from 250 m.sup.2/g to 550 m.sup.2/g, from 250 m.sup.2/g
to 500 m.sup.2/g, from 250 m.sup.2/g to 450 m.sup.2/g, from 250
m.sup.2/g to 400 m.sup.2/g, from 250 m.sup.2/g to 350 m.sup.2/g,
from 250 m.sup.2/g to 300 m.sup.2/g, from 300 m.sup.2/g to 600
m.sup.2/g, from 300 m.sup.2/g to 550 m.sup.2/g, from 300 m.sup.2/g
to 500 m.sup.2/g, from 300 m.sup.2/g to 450 m.sup.2/g, from 300
m.sup.2/g to 400 m.sup.2/g, from 300 m.sup.2/g to 350 m.sup.2/g,
from 350 m.sup.2/g to 600 m.sup.2/g, from 350 m.sup.2/g to 550
m.sup.2/g, from 350 m.sup.2/g to 500 m.sup.2/g, from 350 m.sup.2/g
to 450 m.sup.2/g, from 350 m.sup.2/g to 400 m.sup.2/g, from 400
m.sup.2/g to 600 m.sup.2/g, from 400 m.sup.2/g to 550 m.sup.2/g,
from 400 m.sup.2/g to 500 m.sup.2/g, from 400 m.sup.2/g to 450
m.sup.2/g, from 450 m.sup.2/g to 600 m.sup.2/g, from 450 m.sup.2/g
to 550 m.sup.2/g, from 450 m.sup.2/g to 500 m.sup.2/g, from 500
m.sup.2/g to 600 m.sup.2/g, from 500 m.sup.2/g to 550 m.sup.2/g, or
from 550 m.sup.2/g to 600 m.sup.2/g. The specific surface area of
the silicic acid aggregates may directly correlate to the reaction
rate constant (k) of the reaction between the silicic acid
aggregates and the decomposition products of the alkali metal
salts, as described herein. That is, the greater the specific
surface area of the silicic acid aggregates, the greater the
potential for reaction with the decomposition products present
within the molten salt bath. This may allow for greater control
over the properties of the salt bath composition 408 and increased
chemical durability of the glass article while using fewer silicic
acid aggregates.
[0083] In embodiments, the regeneration medium may include silicic
acid aggregates in an amount sufficient to effectively neutralize
the salt bath composition 408. The Surface Hydrolytic Resistance
(SHR) of a glass article that has been ion exchanged in a molten
may be the most reliably discerning metric for determining the
extent to which the salt bath composition 408 is neutralized. The
Surface Hydrolytic Resistance of a glass article may be measured by
the Surface Glass Test, as detailed in USP <660>. When
measuring the Surface Hydrolytic Resistance of a glass article with
the Surface Glass Test, a glass vial or container composed of the
glass article is filled with carbon dioxide-free or purified water.
The filled vial or container is then subjected to an autoclave
cycle at approximately 121.degree. C. for approximately 1 hour. The
resulting leachate within the vial or container is then titrated to
neutral by a weak hydrochloric acid (e.g., 0.01 M HCl) in the
presence of methyl red. The volume of titrant per 100 mL of
leachate is used to determine the Surface Hydrolytic Resistance of
the glass article. Generally, a greater a titrant volume
corresponds to an inferior chemical durability (that is, the
leachate contains more glass components released by the glass and
thus requires more titrant to offset the change in pH due to the
presence of the glass components). In turn, an inferior chemical
durability generally corresponds to a greater degradation of the
surface of the glass article and a greater concentration of alkali
metal oxides within the salt bath used for ion exchange.
[0084] A low titrant volume and/or high chemical durability may be
desired in strengthened glass articles, particularly strengthened
glass articles intended for use as pharmaceutical packaging.
Generally, a titrant volume less than 1.5 mL is desired for Type I
glasses. However, as described hereinabove, the presence of
decomposition products, such as alkali hydroxides or alkali oxides,
within a molten salt bath used for ion exchange may corrode and/or
etch the surface of the glass article. This etching may result in
increased titrant volumes, which correspond to a decrease in
chemical durability. Typically, the titrant volume of a
strengthened glass article will increase as a function of the time
spent undergoing ion exchange. That is, the longer a glass article
is contacted with a molten salt bath, the greater the titrant
volume. For example, a glass article that undergoes ion exchange
for approximately 3 hours may result in a titrant volume of
approximately 0.9 mL while a glass article that undergoes ion
exchange for approximately 10 hours may result in a titrant volume
of approximately 1.1 mL. As a result, the chemical durability of
strengthened glass articles subjected to ion exchange processes in
a neutralized molten salt may be increased compared to those
subjected to ion exchange processes in a conventional molten salt
(i.e., molten salt that has not been neutralized by silicic acid
aggregates and, as a result, includes alkali hydroxides and/or
alkali oxides).
[0085] In embodiments, particularly in embodiments wherein the salt
bath system is used to strengthen glass articles intended for use
as pharmaceutical packaging, the regeneration medium may include
silicic acid aggregates in an amount from 0.1 wt. % to 10 wt. %
based on the total weight of the salt bath composition. For
example, the regeneration medium may include silicic acid
aggregates in an amount from 0.1 wt. % to 7 wt. %, from 0.1 wt. %
to 5 wt. %, from 0.1 wt. % to 3 wt. %, from 0.1 wt. % to 1 wt. %,
from 0.1 wt. % to 0.5 wt. %, from 0.5 wt. % to 10 wt. %, from 0.5
wt. % to 7 wt. %, from 0.5 wt. % to 5 wt. %, from 0.5 wt. % to 3
wt. %, from 0.5 wt. % to 1 wt. %, from 1 wt. % to 10 wt. %, from 1
wt. % to 7 wt. %, from 1 wt. % to 5 wt. %, from 1 wt. % to 3 wt. %,
from 3 wt. % to 10 wt. %, from 3 wt. % to 7 wt. %, from 3 wt. % to
5 wt. %, from 5 wt. % to 10 wt. %, from 5 wt. % to 7 wt. %, or from
7 wt. % to 10 wt. % based on the total weight of the salt bath
composition. When the regeneration medium includes fewer silicic
acid aggregates (i.e., less than 0.1 wt. %), the entire amount of
the silicic acid may react to unreactive silicates and water before
the molten salt may be effectively neutralized.
[0086] In embodiments, the regeneration medium may include one or
more phosphate salts capable of precipitating excess lithium
cations from the salt bath composition 408. In embodiments, the
phosphate salts may include alkali metal phosphate salts, such as
trisodium phosphate (Na.sub.3PO.sub.4), tripotassium phosphate
(K.sub.3PO.sub.4), dispodium phosphate (Na.sub.2HPO.sub.4),
dipotassium phosphate (K.sub.2HPO.sub.4), sodium triphosphate
(Na.sub.5P.sub.3O.sub.10), potassium triphosphate
(K.sub.5P.sub.3O.sub.10), disodium diphosphate
(Na.sub.2H.sub.2P.sub.2O.sub.7), tetrasodium pyrophosphate
(Na.sub.4P.sub.2O.sub.7), potassium pyrophsophate
(K.sub.4P.sub.207), sodium trimetaphosphate
(Na.sub.3P.sub.3O.sub.9), potassium trimetaphosphate
(K.sub.3P.sub.309), or combinations thereof. In embodiments, the
phosphate salts may include anhydrous phosphate salts, such as
anhydrous trisodium phosphate, which may contain 10 percent (%) or
less water and may have a chemical purity of at least 97% or
greater. As described hereinabove, the phosphate salts may
disassociate into cations, such as sodium and/or potassium cations,
and phosphate anions, which may selectively precipitate lithium
cations to produce insoluble lithium phosphates and maintain a
suitable lithium nitrate concentration in the salt bath composition
408.
[0087] In embodiments, the phosphate salts may have an average
particle size of from 5 .mu.m to 400 .mu.m as measured by laser
diffraction particle size analysis. For example, the phosphate
salts may have an average particle size of from 5 .mu.m to 350
.mu.m, from 5 .mu.m to 300 .mu.m, from 5 .mu.m to 250 .mu.m, from 5
.mu.m to 200 .mu.m, from 5 .mu.m to 50 .mu.m, from 50 .mu.m to 400
.mu.m, from 50 .mu.m to 350 .mu.m, from 50 .mu.m to 300 .mu.m, from
50 .mu.m to 250 .mu.m, from 50 .mu.m to 200 .mu.m, from 200 .mu.m
to 400 .mu.m, from 200 .mu.m to 350 .mu.m, from 200 .mu.m to 300
.mu.m, from 200 .mu.m to 250 .mu.m, from 250 .mu.m to 400 .mu.m,
from 250 .mu.m to 350 .mu.m, from 250 .mu.m to 300 .mu.m, from 300
.mu.m to 400 .mu.m, from 300 .mu.m to 350 .mu.m, or from 350 .mu.m
to 400 .mu.m as measured by laser diffraction particle size
analysis. When the phosphate salts have a smaller average particle
size (e.g., less than 5 .mu.m), any phosphate salts that are
displaced from the containment device, due to any circumstance, may
readily adhere to the surface of glass articles and cause defects
that render the glass articles unsuitable for commercial use.
Moreover, larger average particle sizes (e.g., greater than or
equal to 5 .mu.m) may reduce the solubility of the phosphate salts
in the salt bath composition 408 at ion exchange temperatures and,
in turn, reduce the amount of excess phosphate anions in the molten
salt bath, which may form phosphate crystals on the surface of the
glass articles as discussed hereinabove.
[0088] In embodiments, the regeneration medium may include the
phosphate salts in an amount sufficient to effectively maintain the
concentration of lithium nitrate in the salt bath composition at an
amount less than or equal to 1 wt. % based on the total weight of
the salt bath composition. The regeneration medium may include the
phosphate salts in an amount of from 0.1 wt. % to 10 wt. % based on
the total weight of the salt bath composition. For example, the
regeneration medium may include the phosphate salts in an amount of
from 0.1 wt. % to 7 wt. %, from 0.1 wt. % to 5 wt. %, from 0.1 wt.
% to 3 wt. %, from 0.1 wt. % to 1 wt. %, from 0.1 wt. % to 0.5 wt.
%, from 0.5 wt. % to 10 wt. %, from 0.5 wt. % to 7 wt. %, from 0.5
wt. % to 5 wt. %, from 0.5 wt. % to 3 wt. %, from 0.5 wt. % to 1
wt. %, from 1 wt. % to 10 wt. %, from 1 wt. % to 7 wt. %, from 1
wt. % to 5 wt. %, from 1 wt. % to 3 wt. %, from 3 wt. % to 10 wt.
%, from 3 wt. % to 7 wt. %, from 3 wt. % to 5 wt. %, from 5 wt. %
to 10 wt. %, from 5 wt. % to 7 wt. %, or from 7 wt. % to 10 wt. %
based on the total weight of the salt bath composition. When the
regeneration medium includes the phosphate salts in an amount less
than 0.1 wt. %, all or a substantial portion of the phosphate
anions disassociated from the phosphate salts may precipitate
before the ion exchange process is completed, resulting in the
concentration of lithium cations in the molten salt increasing.
Accordingly, the amount of lithium nitrate in the salt bath
composition 408 increasing to an amount greater than 1 wt. %. In
contrast, when the regeneration medium includes the phosphate salts
in an amount greater than 10 wt. %, the concentration of lithium
nitrate in the salt bath composition 408 may be reduced to an
amount less than 0.01 wt. %, resulting in excess lithium cations
diffusing from the glass articles and an increase in sodium-rich
regions in the glass articles.
[0089] In embodiments, the regeneration medium may include one or
more materials capable of filtering one or more contaminants from
the salt bath composition 408 (also referred to as filtering
media). As used herein, the term "contaminant" refers to debris
that are introduced into the salt bath composition 408 during the
general operation of the salt bath system. That is, contaminants
are any material or compound in the salt bath composition that are
generally considered undesirable and/or may negatively affect the
ion exchange process. Contaminants may include dust/debris, broken
glass pieces, particles created from the corrosion or abrasion of
components of the salt bath system, such as the salt bath tank,
nitrogen oxide species, excess water or combinations thereof. In
embodiments, the filtering media may include porous membranes
and/or matrices, such as, for example, porous metal oxides,
stainless steel powder compacts or screens, porous alumina filters,
porous silica filters, or combinations thereof. The filtering media
may bind and/or trap contaminants while allowing for the relatively
free flow of the salt bath composition 408, effectively filtering
all or a portion of the contaminants from the salt bath composition
408.
[0090] In embodiments, the filtering media may have an average pore
size less than or equal to 20 .mu.m as measured by mercury
intrusion porosimetry (MIP). For example, the filtering media may
have an average pore size of from 0.2 .mu.m to 20 .mu.m, from 0.2
.mu.m to 16 .mu.m, from 0.2 .mu.m to 12 .mu.m, from 0.2 .mu.m to 8
.mu.m, from 0.2 .mu.m to 4 .mu.m, from 0.2 .mu.m to 2 .mu.m, from 2
.mu.m to 20 .mu.m, from 2 .mu.m to 20 .mu.m, from 2 .mu.m to 16
.mu.m, from 2 .mu.m to 12 .mu.m, from 2 .mu.m to 8 .mu.m, from 2
.mu.m to 4 .mu.m, from 4 .mu.m to 20 .mu.m, from 4 .mu.m to 16
.mu.m, from 4 .mu.m to 12 .mu.m, from 4 .mu.m to 8 .mu.m, from 8
.mu.m to 20 .mu.m, from 8 .mu.m to 16 .mu.m, from 8 .mu.m to 12
.mu.m, from 12 .mu.m to 20 .mu.m, from 12 .mu.m to 16 .mu.m, or
from 16 .mu.m to 20 .mu.m as measured by MIP. When the filtering
media have a smaller average pore size (e.g., less than 0.2 .mu.m),
the pressure drop across the filtering media may be too great. In
contrast, when the filtering media may have a larger average pore
size (e.g., greater than 20 .mu.m), a significant amount of the
contaminants may pass through the filtering media without being
filtered from the salt bath composition 408.
[0091] Referring now to FIG. 4C, an expanded view of the
containment device 410 is depicted. As depicted in FIG. 4C, the
containment device may include one or more "regeneration zones"
positioned within the second interior volume 412, each comprising
one or more regeneration media. As used herein, the term
"regeneration zone" refers to a portion of an interior volume that
is at least partially separated from other portions of the interior
volume via a divider and/or barrier. For example, the containment
device 410 depicted in FIG. 4C includes a first regeneration zone
420, a second regeneration zone 422, and a third regeneration zone
424. The containment device 410 depicted in FIG. 4C includes sieves
426a-426d positioned between the regeneration zones, as well as
enclosing the inlet 418 and the outlet 428 of the containment
device 410. The sieves 426a-426d may allow for the flow of the salt
bath composition 408 while also preventing the movement of the
regeneration media through the sieve. In embodiments, the sieves
426a-426d may include openings having effective diameters less than
or equal to 15% of the average particle size of the regeneration
medium. For example, the sieves 426a-426d may include openings
having effective diameters less than or equal to 10%, 5%, or 2.5%
of the average particle size of the regeneration medium. In some
embodiments, the sieves 426a-426d may comprise a mesh having an
average opening size less than the average particle size of the
regeneration media positioned within the second interior volume
412. Accordingly, the one or more sieves may have a mesh number
greater than or equal to 70. In embodiments, the sieves may have a
mesh number of 70, 80, 100, 120, 140, 170, 200, 230, 270, 325, 400,
450, 500, or even 635, based on the American National Standard for
Industrial Wire Cloth (American Standard ASTM-E11). In other
embodiments, the sieves 426a-426d may comprise a porous filtering
device, such as a sintered porous metal, ceramic, or glass, having
an average opening size less than the average particle size of the
regeneration media positioned within the second interior volume
412.
[0092] In embodiments, each regeneration zone may include a
majority of one regeneration medium. For example, in embodiments,
the first regeneration zone 420 may include phosphate salts in an
amount greater than 50 wt. % based on the total weight of the
regeneration media in the first regeneration zone 420, and the
second regeneration zone 422 may include silicic acid aggregates in
an amount greater than 50 wt. % based on the total weight of the
regeneration media in the second regeneration zone 422. In
embodiments, each regeneration zone may include only one
regeneration medium. For example, the first regeneration zone 420
may include phosphate salts in an amount greater than 99 wt. %
based on the total weight of the regeneration media in the first
regeneration zone 420. In other embodiments, each regeneration zone
may be a blend and/or gradient of two or more regeneration
media.
[0093] Referring again to FIGS. 4A-4C, since the regeneration media
are prevented from leaving the regeneration zones, the containment
device 410 may allow for the regeneration (e.g., the precipitation
of excess lithium cations from and/or the neutralization of) the
salt bath composition 408 while also preventing any undesirable
by-products of the regeneration from entering the first interior
volume 404. Accordingly, in embodiments, the portion of the salt
bath composition 408 positioned in the first interior volume 404
and exterior to the second interior volume 410 may be substantially
free of the regeneration media. As used herein, the term
"substantially free" of a compound may refer to a mixture that
comprises less than 0.1 wt. % of the compound. For example, the
salt bath composition, which may be substantially free of
regeneration media, may comprise regeneration media in an amount
less than 0.1 wt. %, less than 0.08 wt. %, less than 0.06 wt. %,
less than 0.04 wt. %, less than 0.02 wt. %, or less than 0.01 wt. %
based on the total weight of the salt bath composition 408.
[0094] Referring again to FIG. 4A, the containment device 410 may
be positioned within the first interior volume 404. However, it
should be understood that other embodiments are contemplated and
possible. Referring to FIG. 4B by way of example, alternatively
and/or additionally, the salt bath system 400 may include a
containment device 410 positioned outside the first interior volume
404. The positioning of the containment device 410 outside the
first interior volume 404 may allow for the regeneration of the
salt bath composition 408 at a temperature less than the ion
exchange temperature of the salt bath composition 408. Without
being bound by any particular theory, it is believed that the
regeneration of the salt bath composition 408 at a temperature less
than the ion exchange temperature of the salt bath composition 408
may increase the efficiency of the one or more regeneration media.
For example, as noted herein, phosphate anions, which have
disassociated from phosphate salts, may selectively precipitate
excess lithium cations to produce lithium phosphate salts. However,
as the temperature of the salt bath composition 408 increases, the
solubility and disassociation of the lithium phosphate salts also
increases and the ability of the phosphate anions to precipitate
lithium cations decreases. Accordingly, the efficiency of the one
or more regeneration media may be maximized in embodiments wherein
the containment device 410 is positioned outside the first interior
volume 404. However, it should be understood that the salt bath
composition 408 should remain a liquid (i.e., a molten salt)
throughout the regeneration process or the salt bath system 400 may
become inoperable due to the inability of the salt bath composition
408 to flow through the containment device 410. Indeed, even if the
salt bath composition 408 remains a liquid albeit having a
significant viscosity, the increased efficiency of the one or more
regeneration media may be outweighed by the reduced flow rate of
the slat bath composition 408 through the containment device
410.
[0095] Referring still to FIGS. 4A-4C, the salt bath system 400 may
include a circulation device 416 proximate to an inlet 418 of the
containment device 410. While the inlet 418 of the containment
device 410 depicted in FIGS. 4A-4C is proximate to the bottom of
the salt bath tank 402, it should be understood that in other
embodiments the inlet 418 of the containment device 410 may be
proximate to the top of the salt bath tank 402. The circulation
device 416 may be operable to to circulate the salt bath
composition 408 through the containment device 410. In operation,
the circulation device may be operable to introduce the salt bath
composition 408 into the inlet 418, through the first regeneration
zone 420, through the second regeneration zone 422, which is
positioned downstream of the first regeneration zone 420, through
the third regeneration zone 422, which is positioned downstream of
the second regeneration zone 422, and out of the containment device
410 through the outlet 428. As used herein, the terms "downstream"
refers to the positioning of components of a system relative to a
direction of flow of materials through the system. For example, a
second component of a system may be considered "downstream" of a
first component of the system if materials flowing through the
system encounter the first component before encountering the second
component. Independent of the circulation of the salt bath
composition 408 through the containment device 410, it is believed
that the circulation of the salt bath composition 408 in the first
interior volume 404 may improve the uniformity and availability of
desirable species throughout the first interior volume 404 and, as
a result, improve the uniformity of the strengthened glass articles
produced by the salt bath system 400.
[0096] The circulation device 416 may include any device suitable
to circulate the salt bath composition 408 through the containment
device 410. For example, the circulation device 416 may include a
pump, such as an electromagnetic pump, an impeller, a gas injection
system, such as an oxygen bubbler, or combinations thereof. The
circulation device 416 may be selected based on various factors,
such as the composition of the salt bath composition 408, the
position of the containment device 410 (e.g., inside and/or outside
of the first interior volume 404 of the salt bath tank 402), and/or
the position of the inlet 418 of the containment device 410 (e.g.,
an impeller may be more suitable for use when the inlet 418 of the
containment device 410 is proximate to the surface of the salt bath
tank 402). In embodiments, the salt bath composition 408 may be
circulated without the need for a mechanical agitator, such as a
pump or impeller. For example, localized areas of the salt bath
composition 408 proximate to the inlet 418 may be selectively
heated, which thermally induce the circulation of the salt bath
composition 408 via buoyancy differences of the selectively heated
portion of the salt bath. In embodiments, the containment device
410 may be coupled directly to the circulation device 416. For
example, in embodiments, such as embodiments wherein the one or
more baskets and/or pouches composed of a stainless steel mesh, the
containment device 410 may be coupled directly to an impeller that
rotates the containment device 410 through the first interior
volume 404 of the salt bath tank 402 and causes the salt bath
composition 408 to circulate through the containment device
410.
[0097] In embodiments, the salt bath composition 408 may be
circulated through the containment device 410 at a rate sufficient
to effectively regenerate the molten salt. Accordingly, the salt
bath composition 408 may be circulated through the containment
device 410 at a rate of from 0.001 vol/hr to 10 vol/hr. Put more
simply, from 0.1% to 2000% of the total volume of the salt bath
composition 408 may be circulated through the containment device
410 every hour. In embodiments, the salt bath composition 408 may
be circulated through the containment device 410 at a rate of from
0.001 vol/hr to 1 vol/hr, from 0.001 vol/hr to 0.1 vol/hr, from
0.001 vol/hr to 0.01 vol/hr, from 0.01 vol/hr to 10 vol/hr, from
0.01 vol/hr to 1 vol/hr, from 0.01 vol/hr to 0.1 vol/hr, from 0.1
vol/hr to 10 vol/hr, from 0.1 vol/hr to 1 vol/hr, or even from 1
vol/hr to 10 vol/hr. When the flow rate of the salt bath
composition 408 through the containment device 410 is too fast
(i.e., greater than 10 vol/hr), the glass articles undergoing ion
exchange in the molten salt may be disturbed, which can result in
glass breakage. Conversely, when the flow rate of the salt bath
composition 408 through the containment device 410 is too slow
(i.e., less than 0.001 vol/hr), the molten salt may not be
regenerated quickly enough to prevent a decrease in the efficacy of
the salt bath.
[0098] In embodiments, the circulation device 416 may be positioned
proximate to the bottom of the salt bath tank 402. Without being
bound by any particular theory, it is believed that contaminants
and/or regeneration medium that has been displaced from the
containment device will generally be denser than the molten salt
and, as a result, will sink to the bottom of the salt bath tank 402
over time. As such, when the circulation device 416 is positioned
proximate to the bottom of the salt bath tank 402, portions of the
molten salt more likely to contain contaminants and loose
regeneration medium will be preferentially circulated through the
containment device 410. This may reduce the number of salt bath
exchanges through the containment device before the molten salt is
regenerated.
[0099] As noted hereinabove, the salt bath composition 408 of the
salt bath system may be heated to an ion exchange temperature to
form a molten salt and one or more glass articles may be submerged
within the molten salt bath in order to effectuate an ion exchange
between the molten salt and the glass articles. Although, for
example, FIGS. 1A and 1B show the glass article 105 completely
immersed in the salt bath 100, it should be understood that, in
embodiments, only a portion of the glass article 105 may be
contacted with the salt bath 100. The glass article 105 may be
brought into contact with the molten salt through immersion in the
salt bath 100, or through spraying, dipping, or other similar means
of contacting the glass article 105 with the salt bath 100. The
glass article 105 may be brought into contact with the salt bath
100 multiple times, including, but not limited to, dipping the
glass article 105 into the salt bath 100
[0100] The glass articles may be contacted with the molten salt for
a treatment time sufficient to create a surface compressive stress
at the surface of the glass article that extends to a depth of
compression. In embodiments, the glass articles may be contacted
with the molten salt bath for a treatment time of from about 20
minutes to about 20 hours. For example, the glass article may be
contacted with the molten salt bath for a treatment time of from
about 20 minutes to about 15 hours, from about 20 minutes to about
10 hours, from about 20 minutes to about 5 hours, from about 20
minutes to about 1 hour, from about 1 hour to about 20 hours, from
about 1 hour to about 15 hours, from about 1 hour to about 10
hours, from about 1 hour to about 5 hours, from about 5 hours to
about 20 hours, from about 5 hours to about 15 hours, from about 5
hours to about 10 hours, from about 10 hours to about 20 hours,
from about 10 hours to about 15 hours, or from about 15 hours to
about 20 hours.
[0101] As the ion exchange process proceeds, the salt bath
composition 408 may be continuously regenerated as described
hereinabove. For example, as the ion exchange process proceeds, the
salt bath composition 408 may be circulated through a containment
device 410, positioned within and/or outside the first interior
volume 404 of the salt bath tank 402, via a circulation device 416.
The circulation of the salt bath composition 408 through the
containment device 410, which may include one or more regeneration
media within the defined interior volume, may remove one or more
impurities from the salt bath composition 408 that formed during
the ion exchange process. Put more simply, the circulation of the
salt bath composition 408 through the containment device 410 may
contact the salt bath composition 408 with the one or more
regeneration media, which may reduce a concentration of one or more
impurities formed during the ion exchange process and continuously
regenerated the salt bath composition 408.
[0102] In embodiments, the glass articles are removed from contact
with the molten salt after the ion exchange process. The resulting
glass article, which has undergone ion exchange, may have a
compressive stress at its surface that extends to a depth of
compression. The compressive stress and depth of compression
increase the resistance of the glass article to breakage following
mechanical insults and, as a result, the glass article may be a
strengthened glass article after the ion exchange process.
EXAMPLES
[0103] The following examples illustrate one or more features of
the present disclosure. It should be understood that these examples
are not intended to limit the scope of the disclosure or the
appended claims.
Example 1
[0104] In Example 1, the concept of the present disclosure was
evaluated on a 10-kilogram scale. A containment/circulation
combination device was prepared including two mesh baskets
constructed of SAE 304 stainless steel, each containing 5 grams of
silicic acid aggregates, attached to a stainless steel impeller,
which, in turn, was attached to a motor. The mesh baskets were then
lowered into 10 kilograms of molten salt consisting of technical
grade potassium nitrate (i.e., greater than 98.5 wt. % potassium
nitrate) and rotated at a rate sufficient to induce a convective
flow through the mesh baskets. Next, 20 batches that included 45
Type I glass vials (as described in U.S. Pat. No. 8,551,898) per
batch were each subjected to an ion exchange process at 470.degree.
C. for 5.5 hours in the molten salt over a period of 29 days at a
rate of approximately 1 ion exchange process per day. The mesh
baskets were removed from the molten salt prior to each ion
exchange process and replaced after each ion exchange process was
completed. After the ion exchange processes were complete, the SHR
of each glass vial was measured by the Surface Glass Test, as
detailed in USP <660>. This process was repeated with 10
batches over a period of approximately 13 days except that no
silicic acid was included in the mesh baskets. The results were
plotted as a function of time and as a function of the number of
glass vials per kilogram of molten salt, and are graphically
depicted in FIGS. 5A and 5B.
[0105] As depicted in FIGS. 5A and 5B, the desired titrant volume
for Type I glasses (approximately 1.3 mL) was exceeded before 7
days elapsed when the mesh baskets did not contain any silicic
acid. That is, when the mesh baskets did not contain any silicic
acid, less than 25 glass vials per kilogram of molten salt were
able to be effectively strengthened. Conversely, when 10 grams
total of silicic acid was included, the desired titrant volume for
Type I glasses was not exceeded until approximately 20 days had
elapsed. That is, when the mesh baskets contained 10 grams of
silicic acid, nearly 70 glass vials per kilogram of molten salt
were able to be effectively strengthened. This indicates that a
regeneration medium including silicic acid may effectively
neutralize a molten salt, even when confined to a single area of
the molten salt. Indeed, the presence of silicic acid nearly
tripled the longevity of the molten salt, which greatly increased
the efficiency of the ion exchange process.
Example 2
[0106] In Example 2, the compressive stresses and depths of
compression of the glass vials of Example 1, which were subjected
to ion exchange processes in the presence of 10 grams total of
silicic acid, were measured. In particular, the compressive
stresses and depths of compression of the glass vials of each batch
were measured and then plotted as a function of time and as a
function of the number of glass vials per kilogram of the molten
salt. The compressive stresses were measured by surface stress
meter (FSM) using commercially available instruments, such as the
FSM-6000 commercially available from Orihara Industrial Co., Ltd.
(Japan). The depths of compression were measured by the same
commercially available instruments at a wavelength of 596 nm. The
results of Example 2 are graphically depicted in FIGS. 6A and
6B.
[0107] As depicted in FIGS. 6A and 6B, the compressive stresses and
depths of compression of the glass vials remained relatively
constant over a period of 30 days of salt bath usage, wherein over
85 glass vials were subjected to the ion exchange process. While
the depths of compression did decrease slightly, the compressive
stresses achieved after 25 days were nearly identical to those
achieved on the first day. This further affirms a regeneration
medium including silicic acid may effectively neutralize a molten
salt, even when confined to a single area of the molten salt.
[0108] It is noted that any two quantitative values assigned to a
property may constitute a range of that property, and all
combinations of ranges formed from all stated quantitative values
of a given property are contemplated in this disclosure.
[0109] It is noted that one or more of the following claims utilize
the term "where" as a transitional phrase. For the purposes of
defining the present technology, it is noted that this term is
introduced in the claims as an open-ended transitional phrase that
is used to introduce a recitation of a series of characteristics of
the structure and should be interpreted in like manner as the more
commonly used open-ended preamble term "comprising."
[0110] Having described the subject matter of the present
disclosure in detail and by reference to specific aspects, it is
noted that the various details of such aspects should not be taken
to imply that these details are essential components of the
aspects. Rather, the claims appended hereto should be taken as the
sole representation of the breadth of the present disclosure and
the corresponding scope of the various aspects described in this
disclosure. Further, it will be apparent that modifications and
variations are possible without departing from the scope of the
appended claims.
* * * * *